Snowboarding is a popular winter sport in which a snowboarder stands atop a snowboard and maneuvers the board over the snow, propelled by gravity. The snowboarder wears boots that are removably attached to the board, with the snowboarder's feet angled with respect to the longitudinal axis of the board and, in some cases, perpendicular to the board axis. The snowboard is controlled by weight transfer and foot movement, both lateral and longitudinal.
A primary skill that must be mastered in snowboarding is the ability to carve a path through the snow, rather than simply sliding over the top of the snow. Carving allows the snowboarder to control the direction and speed of the snowboard. In its simplest execution, a snowboarder carves a path through the snow by shifting his or her weight forward or backward, causing the snowboard to tilt or rotate about its longitudinal axis toward and away from its back side edge. As used herein, front side refers to the side or direction to which the snowboarder's toes are closest and back side refers to the opposite side or direction.
Snowboard boots are conventionally secured to the board using either strap bindings or step-in bindings. In either case, the binding and/or boot usually employs a high back structure that extends upwardly from either the board or the back side of the boot sole, along and behind the ankle of the boot. The high back limits rearward flexure of the ankle so that when the snowboarder leans backwards, force is transmitted to the snowboard tending to rotate the snowboard about its longitudinal axis toward the back side edge. The high back is secured to the board in conventional strap bindings and in high back step-in bindings.
An alternative type of step-in binding is also available, called a plate or flat step-in binding. Flat step-in bindings utilize metal cleats on the bottom of the snowboard boot that mate with a binding structure built into the snowboard, to secure the snowboard boot to the snowboard. For example, two metal cleats are sometimes provided on the bottom of each boot, one toward the front portion of the boot and the other toward the heel of the boot. Step-in bindings provide many advantages over strap and high back step-in bindings, including ease of attachment and disattachment. The flat step-in binding itself, however, does not provide a connection between the snowboarder's calf and the frontside of the snowboard. Therefore, in order to facilitate back side turns, snowboard boots for use with flat step-in bindings are typically much stiffer, particularly along the vertical back portion of the upper, than are snowboard boots for strap and high back step-in bindings. The functional equivalent of the high back is essentially built into the snowboard boot for flat step-in bindings, rigidizing the rear spine of the boot against rear flexion.
The choice of binding type and boot will depend on a variety of factors. For example, in alpine snowboarding, wherein the snowboarder typically maneuvers from the top to the bottom of a snow-covered slope, it is generally preferred to have a stiffer connection between the snowboarder and the snowboard. In free style snowboarding, which typically involves performing more elaborate tricks, more mobility, and flexibility between the snowboarder and the snowboard is desirable. Two or more different pairs of snowboard boots may therefore be necessary for a snowboarder who wants to do both alpine and free style snowboarding—one pair of boots for use with strap or high back step-in bindings; another pair of boots for flat step-in bindings; and possibly a third pair of boots for use with flat step-in bindings that has a greater degree of flexibility in the ankle portion.
In U.S. Pat. No. 5,966,843 to Sand et al., a boot structure is disclosed for use with step-in bindings including an underfoot or shank portion that connects to a heel cup and high back portion. Straps are provided from the high back portion to the shank, whereby backward motion of the high back portion will cause the shank to rise. This boot essentially combines the features of a high back binding and a step-in binding into a soft boot structure.
A similar stiffening assembly is disclosed in U.S. Pat. No. 5,771,609 to Messmer, which teaches a boot insert including a rigid underfoot portion pivotally attached to a rigid back plate, and a pair of flexible tension straps extending between the back plate and the underfoot portion. Neither Messmer nor Sand et al. teaches a stiffening apparatus that can be removed from the boot.
In U.S. Pat. No. 5,606,808, Gilliard et al. teaches a snowboard boot having at least one elongate exterior pocket in the flexible upper portion of the boot with an open top channel to receive a substantially uniform rectilinear cross-sectional elongate stay for stiffening the upper portion of the boot. The stay, which is maintained in the pocket by frictional forces, includes a strap for inserting and removing the stay, whereby the snowboarder can adjust the stiffness of the boot upper portion. The elongate stay does not, however, conform to the shape of the snowboarder's ankle, and is susceptible to being inadvertently pulled out during use—for example, if the snowboarder tumbles in the snow or brushes against obstacles on the slope.
In addition to having need for differing levels of support in the rear of a snowboard boot, there are different snowboarding styles and activities that are facilitated by having a boot with differing levels of stiffness on the anterior side of the ankle, to revise the ease of forward flexure. For example, a snowboarder who rides in a free style fashion, particularly in terrain such as a half pipe or smaller jumps, typically prefers a relatively loose boot with little limitation on forward flexure. Force transmission from the user's lower leg to the toe edge of the board can be finely tuned with a responsive feel, yet requires a high degree of strength for accurate control. In contrast, a snowboarder who rides an all mountain board, particularly at fast speeds, or who tackles very large jumps, typically prefers a boot with a higher degree of stiffness in the forward direction. The wearer is more readily able to maintain control of the toe edge, particularly at high speed, and force may be more efficiently transmitted from the user's lower leg to the toe edge.